Transmit-receive tube



April 4, 1961 J. M. DUFFY ET AL TRANSMIT-RECEIVE TUBE Filed Jan. 21, 1959 INVENTOR. JO HN NLDUF FY HAROLD HEINS United States Patent TRANSMIT-RECEIVE TUBE erly, Mass, a corporation of Massachusetts Filed Jan. 21, 1959, Ser. No. 788,134 2 Claims. (Cl. 315-39) The present invention relates generally to microwave transmission control devices of the gaseous discharge type and more particularly to transmit-receive switching tubes for use in single antenna radar systems.

In present day usage, the transmit-receive tube is conventionally mounted in a radar system to prevent high power transmitted signals from damaging sensitive. receivers by means of an intense gaseous discharge within a resonant structure. Low level received signals, however, are permitted to pass through the tube to the receiver without any ionization of the gas fill. Such tubes, therefore, are commonly provided with microwave frequency permeable dielectric enclosures at the ends of a section of hollow rectangular waveguide to facilitate transmission of the energy. Resonant iris members and discharge gap structures are mounted within the waveguide at spaced intervals. The output end of the transmit-receive tube is conventionally coupled to a section of waveguide plumbing with transition means to a coaxial transmission line for connection to the receiving apparatus.

The invention has for its primary object the provision of a novel transmit-receive tube with integral output transition means incorporated therein.

Another object is the provision of a novel transmitreceive tube with associated output transition means, said tube being of considerably reduced length and weight in comparison with prior art structures.

The invention attains the objects enumerated in a structure featuring the elimination of the conventional output dielectric window in the transmit-receive tube. A continuous non-apertured metallic enclosure is provided at the output end of the tube. An encapsulated bulbous member is introduced through the top broad wall of the waveguide structure at a point intermediate the end enclosure and the last resonant element within the tube. The output coupling means are then introduced into the bulbous member to provide the transition to a coaxial transmission line for connection to the receiving apparatus. The incorporation of the output transition has reduced the length of prior artmicrowave plumbing structures by a factor of 50% and weight by 80%. Accompanying savings in cost, as well as time, in mounting and removal of the structure in the radar system will also follow. The invention accomplishes these advantages without in any manner sacrificing the electrical performance characteristics.

Other objects, features and advantages will become apparent after consideration of the following detailed description and appended drawings, in which:

Fig. l is a perspective View of the illustrative embodiment with a portion of the outer envelope broken away to reveal internal structure;

Fig. 2 is an enlarged cross-sectional view along the longitudinal axis of the envelope; and

Fig. 3 is an end view with the back plate partially removed to reveal the internal structure.

Referring to the drawingsthe illustrative embodiment shown is a broadband transmit-receive tube comprising a assignors to Bomac Laboratories Inc., Bevsection of hollow rectangular waveguide 1 having broad and narrow walls. A metallic plate 2 with a centrally located resonant aperture enclosed by a dielectric window 3 is hermetically sealed at the input end of waveguide section 1. Flange 4 provides means for mounting the tube in appropriate waveguide structure. Plural resonant iris members 5, 6 and 7 are spaced at quarter wavelength intervals along the axis of the waveguide section. Conical members 8, 9 and 10 are introduced through the top broad wall to define with reentrant projections 11 of the iris members plural resonant discharge gaps. An ignitor electrode 12 is introduced through conical men1- ber 10 to provide means for partial ionization of the gaseous atmosphere. The structure described thus far follows conventional transmit-receive tube prior art.

Commonly the transmit-receive tube would be terminated with another plate and window enclosure at the output end. In accordance with the invention, however, we now provide a non-apertured metallic end plate enclosure 13 a quarter of a wavelength away from the last resonant structure to thereby define an effective cavity resonator 14. Spaced at an intermediate point within the resonator 14 is an encapsulated bulbous member 15 sealed to a collar 16 which is in turn sealed to disc 17 secured to the top broad wall. The bulbous member and associated supporting structure will preserve the evacuated condition of the tube and provide access to the resonator 14. A coaxial output fitting 18, such as for example, type N, is then fastened to the disc 17. Such fittings conventionally have a center passageway and the coupling probe member 19 with matching fitting (not shown) is introduced through the passageway.

In a specific embodiment for use at frequencies in the 2500-3000 megacycle range, the probe penetration was determined to be .780 inch down from the top of the waveguide and the probe diameter was .104 inch. The optimum spacing of the probe axis was also ascertained to be approximately .370 inch away from the inner wall surface of the end plate 13. In terms of the operating wavelength this dimension was calculated to be approximately one-twelfth of a guided wavelength (kg) for the selected frequency. The resultant overall tube structure had a length of approximately seven inches as opposed to prior art structure having a length of twelve and one-half inches. The weight reduction is also significant in that the conventional transmit-receive tube with appended transition assembly weighs almost ten pounds while the embodiment of the present invention weighs only three pounds. The results attained with the specific embodiment indicated that electrical performance was well within the specifications for this type. A gaseous atmosphere employed in this illustrative example comprises approximately one millimeter of hydrogen and five millimeters of argon. Similar results as well as advantages will be realized in similar structure at any other desired frequency range in the microwave spectrum.

It has been observed that the Q of the input window may have an effect on the placement of the coaxial probe transition assembly in relation to the end plate. In the illustrative example a very low Q Window was employed having a Q of less than one. For high Q window structures the proper positioning of the probe may be readily determined empirically.

While an illustrative embodiment has been described various alterations or modifications will occur to the skilled artisan. Furthermore, the output probe member may assume numerous other configurations, such as a loop or button. The appended claims should, therefore, be accorded the breadth of interpretation consonant with the spirit and scope of the invention defined therein.

We claim:

1. A transmit-receive tube comprising a vacuum tight aeraeoa waveguide envelope. with an apertured metallic enclosure member disposed at one end thereof, a plurality of resonant iris and discharge gap elements spaced at quarter wavelength intervals along the envelope axis, a solid metallic end wall member enclosing the opposite end of said envelope, an encapsulated dielectric member hermetically sealed to and extending into said envelope from the top broad Wall thereof at a point intermediate to the Wall member and resonant element adjacent thereto, a probe member centrally disposed within said dielectric member to couple electromagnetic wave energy from said waveguide envelope to a coaxial transmission line, the axis of said probe member. being disposed along the longitudinal axis of said envelope approximately onetwelfth of a guided wavelength from the end Wall member for the selected frequency of the transmitted electromagnetic wave energy. 7 l

2. A transmit-receive tube comprising a vacuum-tight rectangular waveguide envelope enclosed at one end by a dielectric window and a solid metallic end Wall memher at the opposite end, plural resonant circuit elements including paired iris plate members and paired discharge gap members spaced at quarter wavelength intervals along the envelope axis, a dielectric bulb member hermetically sealed to the top broad Wall of said waveguide envelope and extending therein more than half the height thereof, probe member centrally disposed within said bulb member to couple electromagnetic wave energy from said waveguide envelope to a coaxial transmission line, the axis of said probe member being disposed along the longitudinal axis of said envelope approximately onetwelfth of a guided wavelength from .theend wall member tor the selected frequency of the transmitted electromagnetic Wave energy.

References Cited in the file of this patent UNITED STATES PATENTS 2,422,190 Fiske June 17, 1947 2,524,268 McCarthy Oct. 3, 1950 2,531,122 Fiske Nov. 21, 1950 2,540,148 Tawney Feb. 6, 1951 2,610,249 Fiske Sept. 9, 1952 2,777,972 Whitmore et al. Jan. 15, 1957 2,903,623 Walker Sept. 8, 1959 2,903,655 Alexander Sept. 8, 1959 

